This renewal grant request is to provide continued support for research exploring the relationships of sodium transport and metabolism in the mammalian renal nephron. The studies proposed in the grant application were designed to study this problem by three different approaches: (1) Effects of inhibitory compounds on renal function and metabolism. (2) Effects of imposed functional changes on the relationships between single nephron function and over-all renal metabolism. (3) Relationships between single nephron function and metabolism as determined from analysis of peritubular capillary blood and tubular fluid. The methods for these studies are those of micropuncture, clearance and extraction using the anaesthetized rat.